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Re: [Discuss-gnuradio] GRC with two URSP2+DBSRX and UHD

From: bobb
Subject: Re: [Discuss-gnuradio] GRC with two URSP2+DBSRX and UHD
Date: Tue, 30 Nov 2010 08:14:32 +0000

>-----Original Message-----
>From: Thomas Hobiger [mailto:address@hidden
>Sent: Tuesday, November 30, 2010 01:04 AM
>To: address@hidden
>Cc: address@hidden, address@hidden
>Subject: Re: [Discuss-gnuradio] GRC with two URSP2+DBSRX and    UHD
>Hi Bob,
>>    This is pretty easy to do (but, I can only tell you how to do it in 
>> C++)...
>>    set_clock_config() in UHD
>Do you have some code snippet to share? Does the C++ version support
>streaming data from a slave device through a host URSP2 before sending
>all data via a single ethernet cable?


  There is no code that I am  aware of that currently does what you want (i.e., 
sync the U2's *and* conveys data from both devices), however, I believe it is 
currently being worked on, however I'm willing to be corrected on this.

  As I said, sync'ing 2 devices to a single PPS signal is pretty 
straightforward, however I think you're looking for more than that.

  Using the "raw" enet drivers the code is essentially...

     usrp2::usrp2::sptr u2 = usrp2::usrp2::make(dev, "");// dev = device path 
(e.g., "eth1")
     // mode = (usrp2::MC_WE_DONT_LOCK + usrp2::MC_PROVIDE_CLK_TO_MIMO) // 
drive clock to cable
                      | (usrp2::MC_WE_LOCK_TO_MIMO) // lock for reference from 
                      | (usrp2::MC_WE_LOCK_TO_SMA) // lock to reference 
provided by front panel

  You need to "do the right thing" on both ends of the cable.

  For UHD (which we're currently transitioning and am still getting up to speed 
with), I believe the equivalent code would be something like:

    uhd::usrp::simple_usrp::sptr u2 = uhd::usrp::simple_usrp::make(dev);
    clock_config_t mode;
    mode.ref_source = { REF_AUTO | REF_INT = 'i' | REF_SMA = 's' | REF_MIMO = 
'm' }l
    mode.pps_source = { PPS_INT | PPS_SMA | PPS_MIMO};
    mode.pps_polarity = { PPS_NEG | PPS_POS};

  As I said, I think what you're actually looking for (clock/pps sync & data 
over the MIMO cable is "in the works", but I could be mistaken).

  Obviously syncing more than 2 usrps requires additional hardware (since 
without additional hardware you can only connect 2 usrps together).

  Hope this helps,


>I am implementing our passive radar in C++ but I thought that GRC is
>nice for testing. I learnt yesterday that things are not completely
>available for GRC. But as our project needs to move on I would be highly
>interested if you can sync (PPS and freq.) two (or more) URSP2s via MIMO
>and (!) stream the data via a single gigabit Ethernet cable with the
>current UHD library? This would enable us to place our receivers at
>arbitrary locations without the need of pulse generators and a 10 MHz
>   Thomas
>Dr. Thomas Hobiger
>Space-Time Measurement Project
>Space-Time Standards Group
>New Generation Network Research Center
>National Institute of Information and Communications Technology
>4-2-1 Nukui-Kitamachi, Koganei
>184-8795 Tokyo
>email:  address@hidden
>phone:  ++81-042-327-7561
>fax:    ++81-042-327-6664
>homepage (priv.): http://www.hobiger.org

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